This invention relates to a plant for electrochemical forming of lead-acid batteries, in particular for large sized industrial type lead-acid batteries, for example stationary batteries for power supply, uninterruptible power supply units, emergency current generators, standby generators, or batteries for power supply systems for driving electrical vehicles, for example forklift trucks, with drawbars.
In the industry for the production of lead-acid batteries, the electrochemical forming of the batteries, that is, the charging of the battery cells with adequate volt and ampere values, is achieved by transforming the inactive material of the cell plates into active material. The electrochemical forming therefore consists in supplying a continuous current to the cell plates of opposite polarity immersed in an electrolyte, generally a solution of sulfuric acid diluted in distilled water.
According to a prior art process for forming the batteries, the cells are firstly filled with an electrolyte with a low concentration of acid and the electrochemical forming of the plates is carried out by supplying a relatively high electrical charging current.
After forming of the plates, the low concentration electrolyte is replaced by an electrolyte with a higher concentration, the same as that used with the battery in operation.
One of the main problems for electrochemical forming of the plates is the increase in temperature of the cells. The temperature of the cells must not exceed 60° Centigrade, that is, 140° Fahrenheit, to prevent the active material of the plates being ruined.
In order to improve the cooling of the cell, a continuous flow of electrolyte is set up which is removed from cells, cooled by a cooling circuit, and then again returned into the cells.
The electrolyte is normally forced into the cell which therefore forces out the electrolyte already present in the cell.
According to the prior art solutions illustrated in FIGS. 1 to 4, special plugs are fitted in the opening of each battery cell.
FIGS. 1 and 2 illustrate a first embodiment of a prior art plug, indicated in its entirety by numeral 1, used to set up the above-mentioned circulation of electrolyte in the cell (not illustrated) during charging.
The plug 1 comprises a first inlet duct 2 through which the electrolyte is introduced inside the cell and a second outlet duct 4 through which the electrolyte is removed from the cell.
The plug 1 also comprises the sealing means 5, to form a seal and to keep it anchored to the opening fitted at the top of the cells to inspect the plates and top up the electrolyte.
According to FIG. 2, the inlet duct 2 has an end 3 which extends inside the cell to a level lower than the inner end of the outlet duct 4.
When the electrolyte, which is in the external circuit, is introduced into the cell through the duct 2, the electrolyte which was already inside the cell automatically flows through the duct 4, thereby creating a continuous flow of electrolyte circulating from the inside of the cell to the outside, and is cooled and then returned to the cell.
FIGS. 3 and 4 illustrate another embodiment of a prior art plug, indicated in its entirety by numeral 6, which is also used in this case to set up the above-mentioned electrolyte circulation, and in which there is also a housing 7 for a probe (not illustrated) to measure the temperature of the electrolyte being removed through duct 4.
Even though it is possible to use a higher charging current if the electrolyte is circulated outside the cells compared with situation with the static electrolyte inside the cells, the operation for electrochemical forming of the plates for industrial type batteries is still quite lengthy, in the order of 140-150 hours.
In particular, with the above-mentioned large sized batteries, the circulation of the electrolyte in the cells cannot exceed certain limits of flow and pressure or head.
In the cells of large sized batteries, the heating caused by the electrical charging and by the overpressure of the forced circulation of the electrolyte can deform the cell casing.
This determines limitations to the possibility to cool the electrolyte and the possibility to exceed certain current charging values for the cells.
Another problem which occurs during the forming of industrial batteries is the development of inflammable gases, especially hydrogen.
Even though there is a continuous flow of electrolyte in the cell, the gas which develops during the forming can stagnate in the upper part of the cell without finding an outlet through the duct 4.
Since the electrolyte in the cell is at an overpressure and at a high temperature, and since short circuits can sometimes be formed between the plates with opposite polarities, with consequent formation of electrical discharges and sparks, the inflammable gas, that is the hydrogen, can explode and destroy the cell.
Yet another problem for the plants for the forming of industrial batteries is the accidental discharge of electrolyte in the event of a fault to the circulation system, in particular in the event of a fault to the circulation pump and the control valves.